Recently, a demand for high-resistance substrate is increased along with the widespread use of a high-frequency communication device used in a short-distance wireless LAN. Conventionally, a compound semiconductor substrate such as GaAs has been mainly used as a support substrate of a RF (Radio Frequency: high frequency) circuit which requires high resistance. However, the compound semiconductor substrate is very expensive.
Meanwhile, a silicon CMOS requires a large amount of power, so that it has been considered that it is not suitable for the RF circuit. However, because of recent considerable miniaturization and development of designing, it can be applied to the RF circuit. Therefore, a high-resistance silicon wafer which is excellent in RF characteristics and excellent in economical efficiency such as a mirror-surface silicon wafer and a SOI (Silicon On Insulator) wafer using high-resistance crystal grown by the Czochralski method (CZ method) has attracted a lot of attention instead of the substrate of the compound semiconductor such as GaAs.
In addition, there is a demand for improvement of a substrate resistance to noise in an analog-digital device and in this view also there is a demand for a high-resistance silicon wafer.
However, since a quartz crucible is used when a silicon single crystal is manufactured by the CZ method, oxygen is contained in the crystal in an oversaturated state. Since an oxygen donor such as a thermal donor (TD) and a new donor (ND) is formed from this oxygen in a heat treatment in the process of forming a circuit of the device, there is a big problem such that resistivity of the wafer unstably varies on the side of a device manufacturer.
FIG. 1 is a graph showing a relation between the oxygen donor and the wafer resistivity. In a case of the normal low-resistance wafer to which a dopant is added, since the oxygen donor slightly affects the resistivity of the wafer, there is no problem in a real operation. However, in a case of the high-resistance wafer in which the dopant is limited, when it is an n type, the resistivity is considerably reduced as the oxygen donor is increased. When it is a p type, although the resistivity is considerably increased along with the increase of the oxygen donor at first, if the oxygen donor is kept increasing, the p type is converted to the n type, so that the resistivity is considerably decreased.
In order to solve the above problem such that the resistivity considerably varies along with the increase of the oxygen donor, there is taken measures to prevent the oxygen donor from being formed by using a low-oxygen silicon wafer which is manufactured using a special crucible in which oxygen is prevented from being fused by a MCZ method or an inner face SiC coating. However, the low-oxygen silicon wafer which needs to use the MCZ method or the special crucible is surely expensive as compared with the general-purpose silicon wafer having a relatively high oxygen concentration which is manufactured by the normal CZ method. In addition, the oxygen lowering has a technical limitation. That is, in general, it is considered that concentration of 6×1017 atoms/cm3 or less is difficult to be implemented and a degree of 8×1017 atoms/cm3 is a limit in a wafer of 300 mm. In addition, in the silicon wafer having a low oxygen concentration, there is a problem of slipping and the like because of the lowering of mechanical strength caused by reduction in oxygen concentration.
In order to solve the above problem, International Publication WO 00/55397 pamphlet discloses a technique in which a silicon single crystal rod having resistivity of 100 Ωcm or more and initial interstitial oxygen concentration of 10 to 25 ppma [JEIDA] (7.9 to 19.8×1017 atoms/cm3 [Old-ASTM]) is grown, and a heat treatment for oxygen precipitation is performed on a silicon wafer cut from the above rod so as to limit the remaining interstitial oxygen concentration in the wafer to 8 ppma [JEIDA] (6.4×1017 atoms/cm3 [Old-ASTM]) or less.
According to this technique, the manufacturing cost of the initial wafer becomes low because the general-purpose silicon wafer having a high initial oxygen concentration is used. Although the general-purpose silicon wafer having the high initial oxygen concentration is used, since the oxygen precipitating heat treatment is performed on the silicon wafer, the remaining oxygen concentration is lowered. Therefore, an oxygen donor is effectively prevented from being generated in a heat treatment for forming a circuit which is to be performed on the side of a device manufacturer. In the process of lowering the oxygen concentration in the wafer, a large amount of oxygen precipitate (BMD) is generated. Therefore, a gettering ability of the wafer is improved.
However, according to the technique disclosed in the International Publication WO 00/55397 pamphlet, it is necessary to generate the large amount of oxygen precipitate (BMD) using a high-resistance primary substrate having a high-oxygen concentration, and to sufficiently lower the remaining oxygen concentration of a product silicon wafer because of generation of the large amount of oxygen precipitate (BMD). However, this causes the following problems.
First, to lower the remaining oxygen concentration in the product silicon wafer causes the mechanical strength of the wafer to be lowered. This is clear from the fact that slip dislocation generated from a wafer supporting part in the heat treatment is fixed by oxygen and as a result, a slip length is lowered as the oxygen concentration is increased [M. Akatsuka et al., Jpn. J. Appl. Phys., 36 (1997) L1422]. Meanwhile, the oxygen precipitate (BMD) is a factor of affecting the strength. The influence of BMD to the strength is complicated. For example, when the heat and stress of one's own weight added to the wafer is not so large, the movement of the slip dislocation is prevented and the strength is improved (International Publication WO 00/55397), but when the heat and the stress of one's own weight is large, the BMD itself becomes a source of the slip dislocation, so that the strength is lowered and the wafer is probably warped (K. Sueoka et al., Jpn. J. Appl. Phys., 36 (1997) 7095). The heat and the stress of one's weight applied to the wafer in the real device process depend on a device structure or a thermal sequence, and it is expected to be increased in some cases. Therefore, in view of maintaining the mechanical strength of the wafer, if the BMD required for gettering is provided, the considerable lowering of the remaining oxygen by the excessive BMD generation described in the International Publication WO 00/55397 is not preferable.
The second problem is a heat treatment cost. That is, in order to generate a large amount of oxygen precipitate, the heat treatment for forming the oxygen precipitate nucleus and the heat treatment for growing the oxygen precipitate at a high temperature for a long time are needed. Therefore, the heat treatment cost is increased. As a result, although the manufacturing cost of the primary wafer is inexpensive, a price of a final product wafer becomes expensive.
It is an object of the present invention to provide the high-resistance silicon wafer in which a gettering ability and economical efficiency is excellent, the oxygen donor is effectively prevented from being generated in the heat treatment for forming the circuit which is to be implemented on the side of the device manufacturer, and mechanical strength is high, and its manufacturing method.